Alkaline electrochemical cell with improved anode and separator components

ABSTRACT

An alkaline electrochemical cell includes a cathode, an anode which includes an anode active material, and a non-conductive separator disposed between the cathode and the anode, wherein from about 20% to about 50% by weight of the anode active material relative to a total amount of anode active material has a particle size of less than about 75 μm, and wherein the separator includes a unitary, cylindrical configuration having an open end, a side wall, and integrally formed closed end disposed distally to the open end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 62/352,243 filed Jun. 20, 2016, the contents of whichare incorporated herein by reference in their entirety.

FIELD

The present technology is generally related to the field of zinc anodesfor electrochemical cells. In particular, the technology is related tozinc anodes with improved reliability and low zinc loadings.

BACKGROUND

Alkaline cells are generally designed to have a defined zinc content inthe anode compartment (zinc loading) which can range from about 65% toabout 72%, depending on discharge capacity needs and costconsiderations. Increasing the zinc loading above 72% can lead toenhanced cell gassing, and decreasing the zinc loading below 65% canlead to reliability issues. Reduced zinc loading can result ininadequate contact between the zinc particles, as well as between theanode and the corresponding current collector. Thus, low zinc loadingsbelow 65% can lead to cell failures in abuse tests such as drop andvibration discharge tests, among others. New and improved ways to reducezinc loading and lower the cost of production without adverselyaffecting the battery performance are needed.

SUMMARY

In one aspect, an alkaline electrochemical cell is provided whichincludes a cathode, an anode comprising an anode active material, and anon-conductive separator disposed between the cathode and the anode,wherein from about 20% to about 50% by weight of the anode activematerial relative to a total amount of anode active material has aparticle size of less than about 75 μm. The separator includes aunitary, cylinder type configuration having an open end, a side wall,and integrally formed closed end disposed distally to the open end. Thistype of separator has an integrated bottom cap (IBC) formed as part ofthe whole separator, unlike conventional separators having a separatecap component at the bottom of the separator.

In some embodiments, the anode active material has an apparent densityfrom about 2.62 g/cc to about 2.92 g/cc. In some embodiments, less thanabout 20% by weight of the anode active material, relative to the totalamount of the anode active material has a particle size of greater thanabout 150 μm. In some embodiments, the anode active material includes azinc alloy. In some embodiments, the zinc alloy includes zinc, indium,and bismuth. In other embodiments, the zinc alloy includes about 130 ppmto about 270 ppm of bismuth; and about 130 ppm to about 270 ppm ofindium. In some embodiments, the anode includes from about 62% to about70% by weight of the zinc alloy, relative to the total weight of theanode. In other embodiments, the anode includes about 63% by weight ofthe zinc alloy, relative to the total weight of the anode.

In one aspect, an anode gel is provided, wherein the gel includes anelectrolyte, a gelling agent, a surfactant compound, and an anode activematerial wherein from about 20% to about 50%, by weight relative to atotal weight of anode active material has a particle size of less thanabout 75 μm.

In some embodiments, about 20% to about 50% by weight of the anodeactive material, relative to the total amount of anode active materialhas a particle size of less than about 75 microns, and about 8% to about20% by weight relative of the total zinc alloy has a particle size ofgreater than about 150 micrometers.

In yet another aspect, a separator is provided, wherein the separatorincludes a non-conductive, porous material formed in to a cylinder andhaving an open end and an integrally formed closed end disposed distallyto the open end, wherein the separator has a single layer wound twiceand having a dry thickness of about 0.205 mm to about 0.245 mm.

In some embodiments, the porous material is a paper composed ofpolyvinyl alcohol fiber, rayon fiber, or cellulose. In some embodimentsthe porous material further includes a surface active agent. In someembodiments, the separator comprises a single coupon of paper woundtwice.

In one aspect a method for reducing the gassing of an electrochemicalcell subject to gassing is provided, wherein the method includesproviding as the active anode of said cell, an anode gel which includesan anode active material, wherein from about 20% to about 50%, by weightrelative to a total weight of anode active material has a particle sizeof less than about 75 μm, an alkaline electrolyte, and a gelling agent.

In another aspect a method for enhancing the discharge performance of anelectrochemical cell is provided, wherein the method includes providingas the active anode of said cell, an anode gel which includes an anodeactive material, wherein from about 20% to about 50%, by weight relativeto a total weight of anode active material has a particle size of lessthan about 75 μm, an alkaline electrolyte, and a gelling agent.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodimentsand features described above, further aspects, embodiments and featureswill become apparent by reference to the following drawings and thedetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a top view and a cross-sectionalview of the IBC a separator constructed, in accordance with oneembodiment.

FIG. 2 is a schematic illustration of an electrochemical cellincorporating an IBC separator constructed, in accordance with oneembodiment.

FIG. 3 is a plot of performance over time of ten LR20 cells that contain63% loading of standard zinc and an integrated bottom cup separator,according to Example 1.

FIG. 4 is a plot of performance over time of ten LR20 cells that contain63% loading of high fines (HF) zinc and an integrated bottom cupseparator, according to Example 1.

FIG. 5 is a plot of performance over time of ten LR20 cells that contain64% loading of standard zinc and an integrated bottom cup separator,according to Example 1.

FIG. 6 is a plot of performance over time of ten LR20 cells that contain64% loading of high fines zinc and an integrated bottom cup separator,according to Example 1.

FIG. 7 shows the mean time to failure (MTTF) for LR20 cells that containan integrated bottom cup separator at different loading, fill level andtype of zinc in the anode, according to Example 1.

FIG. 8 shows the percent of initial amperage after drop test for LR20cells that contain an integrated bottom cup separator, according toExample 1.

FIG. 9 is a graph illustrating gassing characteristics of partiallydischarged (PD) LR20 cells having an integrated bottom cup separator,according to Example 1.

FIG. 10 illustrates the ANSI performance of LR20 cells containing anintegrated bottom cup separator, according to Example 1.

It is to be further noted that the design or configuration of thecomponents presented in these figures are not scale, and/or are intendedfor purposes of illustration only. Accordingly, the design orconfiguration of the components may be other than herein describedwithout departing from the intended scope of the present disclosure.These figures should therefore not be viewed in a limiting sense.

DETAILED DESCRIPTION

Various embodiments are described hereinafter. It should be noted thatthe specific embodiments are not intended as an exhaustive descriptionor as a limitation to the broader aspects discussed herein. One aspectdescribed in conjunction with a particular embodiment is not necessarilylimited to that embodiment and may be practiced with any otherembodiment(s).

As used herein, “about” will be understood by persons of ordinary skillin the art and will vary to some extent depending upon the context inwhich it is used. If there are uses of the term which are not clear topersons of ordinary skill in the art, given the context in which it isused, “about” will mean up to plus or minus 10% of the particular term.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the elements (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein may beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the embodiments and does not pose alimitation on the scope of the claims unless otherwise stated. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential.

Ratio, concentrations, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, 5 to 40 mole % should be interpreted to include not only theexplicitly recited limits of 5 to 40 mole %, but also to includesub-ranges, such as 10 mole % to 30 mole %, 7 mole % to 25 mole %, andso forth, as well as individual amounts, including fractional amounts,within the specified ranges, such as 15.5 mole %, 29.1 mole %, and 12.9mole %, for example.

As used herein, the term “zinc anode” refers to an anode that includeszinc as an anode active material.

As used herein, “fines” are particles passing through a standard 200mesh screen in a normal sieving operation (i.e., with the sieve shakenby hand). “Dust” consists of particles passing through a standard 325mesh screen in a normal sieving operation. “Coarse” consists ofparticles not passing through a standard 100 mesh screen in a normalsieving operation. Mesh sizes and corresponding particle sizes asdescribed here apply to a standard test method for sieve analysis ofmetal powders which is described in ASTM B214.

As used herein, “aspect ratio” refers to the dimension determined by theratio between the length of the longest dimension of the particle andthe relative width of the particle.

As used herein, “unitary” can mean that all the components describedherein are integrally formed as a single unit, and not as separate partsbeing joined to form a unit.

Alkaline batteries have been improved over the years to enhance theirdischarge capability as well as to improve their reliability. However,advances in the technology have been accompanied by enhanced cellgassing. Zinc anode gels of alkaline electrochemical cells are prone toelectrochemical corrosion reactions when the battery cells are stored inthe undischarged or partial discharged condition due to zinc anodecorrosion. Optimized particle size distribution of anode active materialand improved cell component design which will decrease gassing, improvecell discharge, and control cell reliability are desired.

It has now been found that improvement in the reliability of low costalkaline cells can be achieved by inclusion of anode active materialwith a modified particle size distribution in conjunction with aseparator integrated with a bottom cup design. Improvements in cellfunction are achieved by utilizing a zinc powder having an optimizedparticle size distribution (PSD), characterized here as high fines (HF)zinc, alone or in conjunction with a separator designed with anintegrated bottom cup (IBC) separator. The particle size distribution ofthe zinc anode powder is adjusted with respect to the content of dust(<45 μm), fines (<75 μm), coarse (>150 μm), and large particles (>425μm). Conventional alkaline cells use zinc powders with a content of zincfines at or below about 15%, characterized here as STD zinc. In largeLR20 cells, the use of STD fines particles at relatively low levelsresults in reliability failures when the zinc loading is below 65%. Ithas been found that particle to particle contact is favored byincreasing the content of fines above typical standard levels found inconventional battery cells. This is important particularly when usinglow zinc loadings. Lowering the zinc loading in alkaline cells isbeneficial to reduce cost.

Accordingly, in one aspect, an anode gel for an alkaline electrochemicalcell is provided, wherein the anode includes an anode active material,wherein from about 20% to about 50%, by weight relative to a totalweight of anode active material has a particle size of less than about75 μm, an electrolyte, a surfactant, and a gelling agent.

The type of the anode active material may generally be selected fromthose known in the art, in order to optimize performance of the alkalineelectrochemical cell of which this gelled anode is a part. In someembodiments, the anode active material comprises zinc, which may be usedalone or in combination with one or more other metals. Furthermore, itis typically used in the form of an alloy powder. Thus, in someembodiments the anode active material comprises a zinc alloy.

Typically, alloy materials may include from about 0.01% to about 0.5% byweight of alloy agent alone, or in combination with, from about 0.005%to about 0.2% by weight of a second alloying agent such as bismuth,indium, lithium, calcium, aluminum, and the like. For example, in one ormore embodiments one of ordinary skill in the art may readily select asuitable powder comprising zinc mixed with, or alloyed with, one or moreother metals known in the art (e.g., In, Bi, Ca, Al, Pb, etc.).Accordingly, in this regard it is to be noted that, as used herein,“anode active material” and/or “zinc” may refer to a particle or powderalone, or one that has been optionally mixed or alloyed with one or moreother metals. Anode active material particles may be present in avariety of forms including, for example, elongated, round, as well asfiber-like or flake-like particles.

In some embodiments of the present disclosure, the zinc alloy comprisesindium and bismuth. In some embodiments, the zinc alloy includes zinc,bismuth, and indium. In some embodiments, the zinc alloy includes zinc,bismuth, indium, and aluminum. The concentrations of the metals alloyedwith zinc may range from about 20 ppm to about 750 ppm. In someembodiments, the alloying metals are present at a concentration of about50 ppm to 550 ppm. In other embodiments, the alloying metals are presentat a concentration of about 130 ppm to 270 ppm. In other embodiments,the alloying metals are present at a concentration of about 150 ppm to250 ppm. In some embodiments, the zinc alloy includes bismuth and indiumas main alloying elements, each at a concentration of about 130 ppm toabout 270 ppm. In some embodiments, the zinc alloy includes bismuth andindium as main alloying elements, each at a concentration of about 200ppm.

The anode active material can be present in the anode in the form ofcoarse, fines, or dust, for example, or combinations of these forms. Theanode active material may have an average particle size of about 70micrometers to about 175 micrometers. This includes an average particlesize of about 75 micrometers, about 80 micrometers, about 85micrometers, about 90 micrometers, about 100 micrometers, about 110micrometers, about 120 micrometers, about 130 micrometers, about 140micrometers, or about 150 micrometers. In some embodiments, the anodeactive material has an average particle size of about 100 micrometers toabout 170 micrometers. In some embodiments, the anode active materialincludes zinc alloy particles having an average particle size of about120 micrometers.

Standard anode active materials, such as zinc alloy particles (STD)which are conventionally used in electrochemical cells have a particlesize distribution of about 0.5% to about 2.0% dust, about 5% to about25% fines and about 25% to about 60% coarse particles. The integratedbottom cup separator described herein allows for an increase in thecontent of fine zinc anode particles, that is particles passing 200 meshscreen size (75 μm), without concurrent increase in cell gassing.Accordingly, in some embodiments, the negative electrode includes highfines (HF) anode active materials whose fines content is higher andcoarse content is lower than that of conventional standard zinc powders.

In some embodiments, greater than 15% by weight of the anode activematerial, relative to the total amount of anode active material presentin the anode gel, have a particle size of less than about 75micrometers. This includes embodiments wherein greater than about 20%,greater than about 25%, greater than about 30% or greater than about 35%by weight of the anode active material, relative to the total amount ofanode active material present in the anode gel, have a particle size ofless than about 75 micrometers. In some embodiments, about 15% to about60% by weight of the anode active material, relative to the total amountof anode active material present in the anode gel, have a particle sizeof less than about 75 micrometers. This includes embodiments whereinabout 15% to about 55%, about 20% to about 50%, about 25% to about 45%,or about 35% to about 40%, and ranges between any two of these values orless than any of these values, by weight of the anode active material,relative to the total amount of anode active material present in theanode gel, have a particle size of less than about 75 micrometers. Insome embodiments, about 30% by weight of the anode active material,relative to the total amount of anode active material present in theanode gel, have a particle size of less than about 75 micrometers. Insome embodiments, about 40% by weight of the anode active material,relative to the total amount of anode active material present in theanode gel, have a particle size of less than about 75 micrometers. Insome embodiments, about 20% to about 50% by weight of the anode activematerial, relative to the total amount of anode active material presentin the anode gel, have a particle size of less than about 75micrometers.

In some embodiments less than about 35% by weight of the anode activematerial relative to the total amount of anode active material presentin the anode gel has a particle size of greater than about 150micrometers. This includes embodiments wherein less than about 30%, lessthan about 25%, less than about 20% or less than about 15% by weight ofthe anode active material, relative to the total amount of anode activematerial present in the anode gel, have a particle size of greater thanabout 150 micrometers. In some embodiments less than about 20% by weightof the anode active material relative to the total amount of anodeactive material present in the anode gel has a particle size of greaterthan about 150 micrometers.

In some embodiments, about 1% to about 25% by weight of the anode activematerial relative to the total amount of anode active material presentin the anode gel, have a particle size of less than about 45micrometers. This includes embodiments wherein about 1% to about 20%,about 2% to about 15%, or about 5% to about 10%, and ranges between anytwo of these values or less than any of these values, by weight of theanode active material, relative to the total amount of anode activematerial present in the anode gel, have a particle size of less thanabout 45 micrometers. In some embodiments, about 2% to about 10% byweight of the anode active material relative to the total amount ofanode active material present in the anode gel, have a particle size ofless than about 45 micrometers.

A suitable zinc particle size distribution may be one in which at least70% of the particles have a standard mesh-sieved particle size within a100 micron size range and in which the mode of the distribution isbetween about 100 and about 300 microns. In one embodiment, a suitablezinc particle size distribution include particle size distributionsmeeting the above-noted tests and having a mode of 75 microns, 100microns, 150 microns, or 200 microns, each plus or minus about 10%. Inone embodiment, about 70% of the particles are distributed in a sizedistribution range narrower than about 100 microns, for example about 75microns, about 50 microns, or about 40 microns, or less.

The anode gels of the present disclosure may include a zinc loadinglower than the loading in conventional cells. For example, the anodegels may have a zinc loading of about 70% w/w or less, relative to theweight of the anode gel. In some embodiments, the anode gel may have azinc loading of about 68% w/w or less, about 65% w/w or less, about 64%w/w or less, or about 63% w/w or less, relative to the weight of theanode gel. In some embodiments, the anode gel may have a zinc loading ofabout 64% w/w, relative to the weight of the anode gel. In otherembodiments, the anode gel may have a zinc loading of about 63% w/w,relative to the weight of the anode gel.

The anode gel materials have a suitable viscosity required to providethe enhanced cell discharge performance. For example, the viscosity maybe from about 30,000 cps to about 200,000 cps, at about 25° C.

The anode gel of the present disclosure includes an alkalineelectrolyte, and in some embodiments an alkaline electrolyte having arelatively low hydroxide content. Suitable alkaline electrolytesinclude, for example, aqueous solutions of potassium hydroxide, sodiumhydroxide, lithium hydroxide, as well as combinations thereof. In oneparticular embodiment, however, a potassium hydroxide-containingelectrolyte is used. In other embodiments, the alkaline electrolyteincludes water and potassium hydroxide.

The electrolytes utilized in accordance with the present disclosuretypically have a hydroxide (e.g., potassium hydroxide) concentration ofabout 35%, about 30% or less (e.g., about 29%, about 28%, about 27%,about 26%, or even about 25%), based on the total electrolyte weight.However, typically the electrolyte has a hydroxide concentration ofbetween about 25% and about 35%, or between about 26% and about 30%. Inone particular embodiment (e.g., a anode gel suitable for use in a cellsized and shaped as, for example, an AA or AAA cell), the hydroxideconcentration of the electrolyte is about 28% by weight, based on thetotal weight of the electrolyte.

In some embodiments, the hydroxide electrolyte content in the anode gelis generally at or near that of conventional gelled anodes, theconcentration for example is at least about 24% by weight, at leastabout 26% by weight, or at least about 28% by weight, and less thanabout 34% by weight, less than about 32% by weight, or less than about30% by weight, based on the total weight of the gelled anode. Theconcentration of the electrolyte in the anode gel of the presentdisclosure may, therefore, typically be within the range of from about24% by weight to about 34% by weight, from about 26% by weight to about32% by weight, or from about 28% by weight to about 31% by weight, basedon the total weight of the anode gel. The desired concentration ofelectrolyte in the anode gel generally depends on a variety of factorsincluding, for example, the concentration of zinc in the gelled anode.

The gelling agent is present in the anode, at least in part, to addmechanical structure and/or to coat the metallic particles to improveionic conductivity within the anode during discharge. Suitable gellingagents are those that impart a rigid-type gel structure and a slightlydecreased packing density to the gelled anode within the cell, as wellas a corresponding greater but more stable anode particle-to-particledistance. The anode may be prepared by formulating an electrolyte,preparing a coated metal anode which includes the gelling agent, andthen combining the electrolyte and the coated metal anode to form aanode gel. The gelling agent of the present disclosure may include, forexample, a highly cross-linked, polymeric chemical compound that hasnegatively charged acid groups, such as a polyacrylic acid gelling agenthaving a high degree of crosslinking.). Highly crosslinked polyacrylicacid gelling agents, commercially available under the name Carbopol™(Carbopol 940, Carbopol 934, Carbopol 674) from Lubrizol Corporation(Wickliffe, Ohio) as well as Flogel™ (e.g., Flogel™ 700 or 800) from SNFHolding Company (Riceboro, Ga.), among others, are suitable for use inaccordance with the present disclosure.

Suitable gelling agents may be selected based on various characteristicssuch as the degree of crosslinking, the viscosity and/or density. Theconcentration of the gelling agent in the anode gel may be optimized fora given use. For example, the concentration of the gelling agent is atleast about 0.30 weight %, based on the total weight of the anode gel,including at least about 0.40 weight %, at least about 0.50 weight %, atleast about 0.60 weight %, at least about 0.625 weight %, at least about0.65 weight %, at least about 0.675 weight %, at least about 0.7 weight% or more. For example, in various embodiments the concentration of thegelling agent in the gelled anode may be from about 0.40% to about0.75%, or between about 0.50% and 0.75%, or between about 0.6% and about0.7%, or between about 0.625% and about 0.675%, by weight of the anodegel.

The anode gel may include other components or additives, in addition tothe anode active material, the gelling agent and the electrolyte. Suchadditives include, for example, absorbents, corrosion inhibitors orgassing inhibitor etc. Suitable absorbent materials may be selected fromthose generally known in the art. Exemplary absorbent materials includethose sold under the trade name Salsorb™ or Alcasorb™ (e.g., Alcasorb™CL15), which are commercially available from Ciba Specialty (CarolStream, Ill.), or alternatively those sold under the trade nameSunfresh™ (e.g., Sunfresh DK200VB), commercially available from SanyoChemical Industries (Japan). Suitable gassing inhibitors include organicphosphate esters, for example, RHODAFAC® RM-510 and RHODAFAC® RS-610,which are commercially available from Rhodia (Boston, Mass.).

It has been surprisingly found by the present disclosure that high finesanode active material particles improve packing, enhanceparticle-to-particle contact, and increase active anode reaction sitesthat are necessary for high drain capability.

Accordingly, in some embodiments of the present disclosure, the anodeactive material has an apparent density below about 3.00 g/cc. In otherembodiments, the anode active material has an apparent density of fromabout 2.55 g/cc to about 2.99 g/cc, in some embodiments from about 2.60g/cc to about 2.95 g/cc, in some embodiments about 2.62 g/cc to about2.95 g/cc, in some embodiments about 2.65 g/cc to about 2.90 g/cc, andin some embodiments about 2.70 g/cc to about 2.85 g/cc. In yet otherembodiments, the anode active material has an apparent density of about2.71 g/cc; in some embodiments about 2.83 g/cc; and in some embodimentsabout 2.94 g/cc. In still other embodiments, the anode active materialhas an average apparent density of about 2.70 g/cc; in other embodimentsan average apparent density of about 2.80 g/cc; and in yet otherembodiments an average apparent density of about 2.95 g/cc.

The technology provides an anode gel having yield stress of greater thanabout 150 cps. This includes yield stress of from about 150 to about950, and ranges between any two of these values or less than any one ofthese values. In some embodiments, the anode gel has a yield stressvalue of about 250 N/m² to about 850 cps.

The anode gel of the disclosed embodiments may be included as acomponent in a conventional electrochemical cell such as batteries.These include, for example, alkaline cylindrical cells, e.g., zinc-metaloxide cell, as well as galvanic cells, such as in metal-air cells, e.g.,zinc-air cell. Among the cylindrical metal-metal oxide cells andmetal-air cells, the anode material is applicable to those shaped forAA, AAA, AAAA, C, or D cells. Metal-air cells which include the anodedescribed herein may usefully be constructed as button cells for thevarious applications such as hearing aid batteries, and in watches,clocks, timers, calculators, laser pointers, toys, and other novelties.Also, the anode may find application in any metal air cell using flat,bent, or cylindrical electrodes. Use of the anode material as componentsin other forms of electrochemical cells is also contemplated.

Accordingly, in one aspect, provided is an alkaline electrochemical cellwhich includes a cathode, an anode which includes an anode activematerial, and a non-conductive separator disposed between the cathodeand the anode. In some embodiments of the electrochemical cell, about20% to about 50% by weight of the anode active material relative to atotal amount of anode active material has a particle size of less thanabout 75 μm. In some embodiments of the electrochemical cell, theseparator includes a unitary, cylinder type configuration having an openend, a side wall, and integrally formed closed end disposed distally tothe open end.

An exemplary embodiment of an alkaline electrochemical cell isillustrated in FIG. 2, although other designs should not be so limited.Referring initially to FIG. 2, the electrochemical cell comprise acentrally disposed anode (i.e., a negative electrode) surrounded by anelongate annular cathode (i.e., a positive electrode). The anode andcathode are disposed in close, but physically spaced relation with eachother within a metal container (which serves as a positive currentcollector) having an open top end. A tubular separator (also sometimesreferred to as an anode container) is formed as a cup to hold the anodematerial and physically separates the anode and cathode within the metalcontainer.

Electrical connection to the anode is achieved by inserting an elongatemetal rod or wire, commonly referred to as a negative current collector,into the anode. A top end of the current collector protrudes above thegasket for physical and electrical connection to an electricallyconductive negative terminal plate, while the primary length of thecollector below the gasket is inserted into the anode material. Thegasket seals the collector at the gasket hub, through which thecollector extends, to inhibit anode material from passing out throughthe gasket.

In a conventional electrochemical cell, the separator extends from thebottom of the metal container to a terminal end extending slightlyoutward from between the anode and the cathode, particularly prior tothe cell being closed. Upon closing the cell, the gasket contacts andpushes down against the terminal end of the separator, often causing theterminal end of the separator to generally fold or bend so that one sideof the terminal end of the separator generally faces and abuts againstthe gasket to inhibit electrolyte or particulate material (e.g., theelectrode materials) against leaking or being carried over the terminalend of the separator between the anode and cathode compartments. Furtherthe thick separator takes up space within the cell and thus compromisesthe quantity of active materials that can be incorporated in the cell.As long as adequate electrolyte is available in the cell, the quantityof active materials and the efficiency of their discharge determine theservice life of the cell. The IBC Separator described herein reduces thevolume occupied by the separator, e.g., by decreasing the separator wallthickness and reduces cost by eliminating the use of the bottom disk.

The electrochemical cell may be prepared by any means known in the art,so long as the resulting cell does not conflict with the disclosurespresented herein. Thus, the present disclosure includes a method ofpreparing a electrochemical cell including the components and theirrespective concentrations as discussed throughout the entirety of thisdisclosure.

The anode for the electrochemical cell is as described hereinabove. Thecathode of the electrochemical cell may include any cathode activematerial generally recognized in the art for use in alkalineelectrochemical cells. The cathode active material may be amorphous orcrystalline, or a mixture of amorphous and crystalline. For example, thecathode active material may include, or be selected from, an oxide ofcopper, an oxide of manganese as electrolytic, chemical, or natural type(e.g., EMD, CMD, NMD, or a mixture of any two or more thereof), an oxideof silver, and/or an oxide or hydroxide of nickel, as well as a mixtureof two or more of these oxides or hydroxide. Suitable examples ofpositive electrode materials include, but are not limited to, MnO₂ (EMD,CMD, NMD, and mixtures thereof), NiO, NiOOH, Cu(OH)₂, cobalt oxide,PbO₂, AgO, Ag₂O, Ag₂Cu₂O₃, CuAgO₂, CuMnO₂, Cu Mn₂O₄, Cu₂MnO₄,Cu_(3-x)Mn_(x)O₃, Cu_(1-x)Mn_(x)O₂, Cu_(2-x)Mn_(x)O₂(where x<2),Cu_(3-x)Mn_(x)O₄ (where x<3), Cu₂Ag₂O₄, or a combination of any two ormore thereof.

The electrochemical cell may include a separator between the cathode andthe zinc anode, which is designed for preventing short-circuitingbetween the two electrodes. Generally, any separator material and/orconfiguration suitable for use in an alkaline electrochemical cell, andwith the cathode and/or anode materials set forth herein above, may beused in accordance with the present disclosure. In one embodiment, theelectrochemical cell includes an integrated bottom cup separator systemthat is disposed between a gelled anode of the type described here and acathode.

In one aspect, provided is a separator for an electrochemical cell,wherein the separator includes a non-conductive, porous material formedin to a cylinder and having an open end and an integrally formed closedend disposed distally to the open end.

As described above, in conventional separators, one end of the separatorhas a bottom disk folded to form a cup shaped separator which extends into the bottom of the cell cavity holding the anode gel and insulating itfrom the metal battery container as well as from the cathode. Thisconfiguration generally requires multiple coupons of separator materialhaving multiple wraps, for example 2 coupons having 2 wraps (2×2). Theseparator of the present disclosure is designed to the have anintegrated bottom cup (IBC), which when used in electrochemical cells,especially in large cells such as LR20, provides benefits such as costreduction by eliminating the use of the bottom disk, containment of theanode gel within the separator unit to improve reliability, andreduction in paper volume from multiple coupons having multiple wraps(e.g., 2×2) to a single coupon having one or more wraps (e.g., 1×2),thus increasing internal anode volume. The anode and separator designenhancements were found to result in improved properties such as forreduced cost and reliability.

Referring to FIG. 1, in an exemplary embodiment for an IBC separator forLR20 cells, the separator 10 includes a unitary, cylindrical body havingan open end 20, a side wall 30, and integrally formed closed end 40disposed distally to the open end. The separator is prepared by windinga single coupon of separator material, such as paper, once or twicearound a mandrel, and having multiple pleats formed and folded inward onone end to form a flat closed end. The closed end is permanently bondedtogether using suitable sealing methods such as by utilizing atomizedwater, heat, and/or pressure. Typically, the separator 10 is formed andassembled into an electrochemical cell during the cell assembly withoutthe use of glue or other adhesives. However, adhesives and/or sealantscould be applied to the separator, if required.

The separator may be made of any suitable alkaline resistant,non-conductive synthetic or natural, woven or non-woven porous material,including, but not limited to, polymer materials, Tencel® (lyocell),mercerized wood pulp, polypropylene, polyethylene, cellophane,cellulose, methylcellulose, rayon, nylon and combinations thereof. Insome embodiments, the separator is composed of a porous material whichincludes a paper composed of one or more polymeric fibers. In someembodiments, the separator a porous material which includes one or morepolymer fibers with an effective amount of a surface active agentembedded therein. Suitable polymer materials for the polymeric fiberinclude, but are not limited to, polyvinyl alcohol, polyamides,polyethylene terephthalate, polypropylene terephthalate, polybutyleneterephthalate, polyvinylidene fluoride, polyacrylonitrile,polypropylene, polyethylene, polyurethane and blends, mixtures andcopolymers thereof such as rayon, nylon, and the like and combinationsthereof.

In some embodiments, the porous material includes paper. In someembodiments, the porous material includes a paper which includespolyvinyl alcohol fiber, rayon fiber, cellulose, or a combination of twoor more thereof, and can have a surface active agent.

The active surface agent can include, but are not limited to ionicsurfactants and nonionic surfactants. The amount of the surface activeagent can vary from about 0.2 wt % to about 1.0 wt % relative to thepolymer material.

In some embodiments, the IBC separator may be designed to include asingle layer of the non-conductive porous material sheet wound twice.The IBC separator may have a thickness, when measured in the dry state(dry thickness) of less than about 0.3 mm, this includes a dry thicknessof less than about 0.29 mm, less than about 0.28 mm, less than about0.27 mm, less than about 0.26 mm, or less than about 0.25 mm. In someembodiments, the IBC separator has thickness in a dry state of about0.15 mm to about 0.26 mm, which includes about 0.18 mm to about 0.25 mm,about 0.205 mm to about 0.245 mm, about 0.210 mm to about 0.240 mm, orabout 0.215 mm to about 0.235 mm, and ranges between any two of thesevalues or less than any one of these values. In some embodiments, theIBC separator has thickness in a dry state of about 0.205 mm to about0.245 mm, when measured using a micrometer instrument according to ISOStandard 534 at a pressure of 100 kPa and 20 kPa.

The anode and separator design embodiments detailed in the presentdisclosure allows reducing the zinc loading in alkaline cells to as lowas 63%, or lower, by adjusting the zinc particle size distribution tospecified levels of dust, fines, coarse, and large particles. Drop anddischarge vibration failures in large cells can be suppressed bycontrolling the level of fines particles to be above about 20% byweight. Cell gassing, such as after partial battery discharge, isimpacted by the content of zinc fines particles. The anticipated highcell gassing from the enlarged surface area with increased levels offines is suppressed by controlling the level of coarse particles. Themechanisms leading to gas suppression in an alkaline cell havingrelatively high content of fines is based on minimizing the adverseimpact of metallic impurities within the battery by controlling thecontent of coarse zinc particles.

Reliability failures at relatively low zinc loadings are thought to bethe result of insufficient particle-to-particle contact between the zincparticles which leads to low amperage, voltage dips, and failures duringdischarge vibration. Particle-to-particle contact can be improved byincreasing the content of zinc fine particles in the anode batteryelectrode, as disclosed here. The zinc anode powder with increasedlevels of fines can be contained in a separator whose design has abottom cup integrated in the battery separator as a whole. The use ofIBC separator with conventional zinc powder material in battery cells,such as LR20 cells, at low zinc loadings, such as below 65%, results inbattery failures during abuse testing. However, by using an HF zinc typepowder in conjunction with IBC separator in LR20 cells the battery costcan be reduced and its reliability issues eliminated, as described inthe examples below.

As further detailed elsewhere herein, the electrochemical cells of thepresent disclosure have been observed to exhibit improved performancecharacteristics, which may be measured or tested in accordance withseveral methods under the American National Standards Institute (ANSI).Results of various tests of cells of the present disclosure are detailedbelow in the Examples.

The following Examples describe various embodiments of the presentdisclosure. Other embodiments within the scope of the appended claimswill be apparent to a skilled artisan considering the specification orpractice of the disclosure provided herein. It is therefore intendedthat the specification, together with the Examples, be consideredexemplary only, with the scope and spirit of the disclosure beingindicated by the claims, which follow the Examples.

EXAMPLES

In the Examples presented below, electrochemical cells of the presentdisclosure were tested for DSC performance, drop test amperage (bothbefore and after the drop), partial discharge gassing and conditionsafter storage.

Example 1 Performance of Electrochemical Cells with Anode Containing HFZinc and IBC Separator

In the Examples presented below, electrochemical cells were tested forDSC performance, partial discharge cell gassing, undischarged cellgassing, and conditions after storage. Gelled anodes were prepared inaccordance with the improvements of the present disclosure.

Gel viscosity is measured using Brookfield digital viscometer andteflon-coated spindle #06 at 4 rpm. When measuring, allow the reading tostabilize over 5 minutes before recording the viscosity value.

For yield stress value measurement, measuring the gel viscosity valuesat 1.0 rpm (R1) and 0.5 rpm (R2) respectively, the yield stress value iscalculated using the formula: yield stress value=(R2−R1)/100.

FIG. 3 shows the discharge vibration of LR20 battery cells made withstandard bismuth-indium zinc alloy powder (STD) of apparent density at3.0 g/cc and containing 12% of zinc fines particles (<75 μm), 45% ofcoarse particles (>150 μm), and at a zinc loading of 63%. The anode gelsof the LR20 cells had a gel KOH concentration at 32% and the zinc powderhad bismuth and indium as main alloying elements at a concentration ofabout 150 ppm and 150 ppm, respectively. The discharge vibration test isdone applying to each battery a continuous discharge resistance load of1.5 ohms while the batteries are kept in place in a vibration tableapplying a simple harmonic motion with an amplitude of 0.75 mm at afrequency of 10 Hz which is increased to a maximum of 40 Hz at a rate of1 Hz per minute. The discharge cycle is completed over a period of 30minutes. FIG. 4 displays the discharge vibration data of a similar cellas described in FIG. 3 with a zinc loading at 63%, except that thebismuth-indium zinc alloy powder has an apparent density at 2.80 g/ccand contains 40% of fines particles and 11% of coarse particles,referred here as an HF type zinc powder. FIG. 4 shows that dischargevibration failures, defined by the drop in cell voltage (OCV) below 1 Vafter 30 min of discharge, is eliminated when HF zinc is used.

FIG. 5 shows the discharge vibration of LR20 battery cells containingstandard bismuth-indium zinc alloy powder (STD) as described in FIG. 3,except that the zinc loading is 64%. FIG. 6 shows the dischargevibration of LR20 battery cells as described in FIG. 5, except that theanode zinc is HF zinc at the loading of 64%. It is seen the failureswith STD zinc persists at 64%, but it is eliminated with HF zinc at thiszinc loading.

In addition to type of zinc based on particle size distribution, othersfactors impacting cell failure due to discharge vibration are zincloading and anode gel fill, as shown in FIG. 7. This figure shows themean time to failure during discharge vibration as affected by zincloading, anode gel fill, and type of zinc powder. The respective pvalues for each of the tested factors is below 0.050 and indicate thatdischarge failures are suppressed by increasing zinc loading, increasinggel fill, and particularly by using HF type zinc. The lower the p valuebelow 0.05, the greater the statistical significance of the testedfactor. Another beneficial effect of using HF type powder is suppressionin drop test failures. The drop test consist in recording the shortcircuit current (Flash Amps) and open circuit voltage (OCV) beforerolling each battery of a flat surface five times consecutively from aheight of 102 cm onto a vinyl covered floor. After letting the batteryto rest for one hour, the final Flash Amp and OCV values are recorded.For LR20 cells, to pass the drop test, the minimum % of initial Amps is50%.

FIG. 8 shows the drop test data of LR20 cells made with IBC separatorsand indicates that cells having HF zinc pass the test, unlike the caseof cells made using conventional STD zinc. Cell gassing after partialdischarge of the referred LR20 cells having HF or STD zinc at 63% and64% with anode fill gels at 2% and 5.7% is shown in FIG. 9. No adversegassing impact with the use of HF zinc is seen. Also, performance is notadversely impacted with the use of HF zinc, as shown in FIG. 10.

While certain embodiments have been illustrated and described, it shouldbe understood that changes and modifications can be made therein inaccordance with ordinary skill in the art without departing from thetechnology in its broader aspects as defined in the following claims.

The embodiments, illustratively described herein may suitably bepracticed in the absence of any element or elements, limitation orlimitations, not specifically disclosed herein. Thus, for example, theterms “comprising,” “including,” “containing,” etc. shall be readexpansively and without limitation. Additionally, the terms andexpressions employed herein have been used as terms of description andnot of limitation, and there is no intention in the use of such termsand expressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the claimed technology.Additionally, the phrase “consisting essentially of” will be understoodto include those elements specifically recited and those additionalelements that do not materially affect the basic and novelcharacteristics of the claimed technology. The phrase “consisting of”excludes any element not specified.

The present disclosure is not to be limited in terms of the particularembodiments described in this application. Many modifications andvariations can be made without departing from its spirit and scope, aswill be apparent to those skilled in the art. Functionally equivalentmethods and compositions within the scope of the disclosure, in additionto those enumerated herein, will be apparent to those skilled in the artfrom the foregoing descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods, reagents, compounds compositions or biologicalsystems, which can of course vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the like,include the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

All publications, patent applications, issued patents, and otherdocuments referred to in this specification are herein incorporated byreference as if each individual publication, patent application, issuedpatent, or other document was specifically and individually indicated tobe incorporated by reference in its entirety. Definitions that arecontained in text incorporated by reference are excluded to the extentthat they contradict definitions in this disclosure.

Other embodiments are set forth in the following claims.

What is claimed is:
 1. An alkaline electrochemical cell comprising: acathode; an anode comprising an anode active material; and anon-conductive separator disposed between the cathode and the anode;wherein: from about 20% to about 50% by weight of the anode activematerial relative to a total amount of anode active material has aparticle size of less than about 75 μm, and less than about 20% byweight of the anode active material, relative to the total amount of theanode active material, has a particle size of greater than about 150 μm;and the separator comprises a unitary, cylindrical configuration havingan open end, a side wall, and an integrally formed closed end disposeddistally to the open end.
 2. The alkaline electrochemical cell of claim1, wherein the anode active material has an apparent density from about2.62 g/cc to about 2.92 g/cc.
 3. The alkaline electrochemical cell ofclaim 1, wherein the anode active material comprises a zinc alloy,wherein the zinc alloy comprises zinc, indium, and bismuth.
 4. Thealkaline electrochemical cell of claim 3, wherein the zinc alloycomprises: about 130 ppm to about 270 ppm of bismuth; and about 130 ppmto about 270 ppm of indium.
 5. The cell of claim 3, wherein the zincalloy is present in the anode from about 62% to about 70% by weight,relative to the total weight of the anode.
 6. The cell of claim 3,wherein the zinc alloy is present in the anode at about 63% by weightrelative to the total weight of the anode.